1. Field of the Invention
The present invention relates to a drive apparatus for a self light-emitting display unit.
2. Description of the Related Art
As a method of allowing a plasma display panel as a self light-emitting display unit to present gradation display, there is known a method which divides the display period of one frame (field) into N sub-frames (sub-fields) to permit light emission only for the time corresponding to the weight on each bit position of N-bit display data (so-called sub-field method).
When pixel data consists of eight bits, for example, the display period of one frame is divided to eight sub-frames SF8, SF7, SF6, . . . , and SF1 in the order of a heavier weight to a lighter one. At this time, light emissions of 128 pulses, 64 pulses, 32 pulses, 16 pulses, 8 pulses, 4 pulses, 2 pulses and 1 pulse are carried out in the respective sub-frames SF8 to SF1. The light emissions in those eight sub-frames provide 256-gradation display.
This gradation display scheme however has such a problem that a more-like false outline which looks like a gradation-lost image is observed near the area on a flat image where the gradation level crosses the boundary of 2.sup.n gradation levels, such as 128 or 64, which significantly degrades the display quality.
Japanese Unexamined Patent Publication No. Hei 7-271325 has proposed a gradation display scheme of equally dividing a sub-frame with a heavy weight into a plurality of sub-frames, separating them so as to prepare a plurality of light emission patterns which have the equal light emission time (the equal number of light emissions) but different light emission orders of the sub-frames, and changing the light emission pattern from one to another pixel by pixel (pseudo outline compensation data conversion) to suppress a pseudo outline.
This gradation display scheme however suffers an increased number of sub-frames in one frame period. Further, if the number of bits of pixel data is increased to improve the image quality, the number of sub-frames in one frame period is increased more.
The increase in the number of sub-frames in one frame period increases the addressing period for lighting a plasma display panel for light emission. This relatively shortens the sustain period as the light emission period, reducing the maximum luminescent.
In this respect, a dithering process which reduces the number of bits (the number of sub-frames) of pixel data and effects pseudo intermediate tone display is performed.
The dithering process expresses a single intermediate display level based on plural pieces of pixel data adjacent to one another. In the case where 8-bit equivalent gradation display is demonstrated using the upper six bits of pixel data in 8-bit pixel data, for example, first, dither coefficients different pixel by pixel in each set of four pixels adjoining right and left and up and down are added to pixel data. Then, the upper six bits of the dither-coefficients added pixel data are extracted to be used as a drive signal for the display panel. This dithering process generates a combination of four different intermediate display levels with four pixels, thus ensuring four times the 6-bit gradation display levels or 8-bit equivalent intermediate tone display.
In the case where an image is displayed on a plasma display based on video signals obtained by interlaced scanning as done in the NTSC system or the high vision system or the like, to compensate a low luminescent of emitted light, pixel data corresponding to odd rows (even rows) of the screen is also assigned directly to even rows (odd rows) for interpolation to drive the display by sequential scanning (linear scanning).
When linear scanning is carried out in the above-described manner after performing the aforementioned pseudo outline compensation data conversion and dithering process, light is emitted from two pixels, arranged in the vertical direction, based on the same pixel data. This raises a problem that dithering-oriented noise, dot interference caused by the pseudo outline compensation and the like are likely to appear more prominently.